Dropzone.js + Stimulus + Active Storage + CSS Zero (2025)

_form.html.erb

<%= form_with(model: billboard) do |form| %>
  <%= tag.div class: "dropzone", data: { controller: "dropzone", dropzone_param_name_value: "billboard[images][]", dropzone_url_value: rails_direct_uploads_url, dropzone_accepted_files_value: "image/*", dropzone_max_files_value: 3, dropzone_max_filesize_value: 0.300 } do %>
    <div class="dz-default dz-message flex flex-col items-center">
      <%= image_tag "upload.svg", size: 28, class: "colorize-black", aria: { hidden: true } %>
      <h5 class="font-semibold mbs-4">Drop files here or click to upload.</h5>
      <p class="text-sm text-subtle">Upload up to 10 files.</p>
    </div>
  <% end %>

  <div class="inline-flex items-center mbs-2 mie-1">
    <%= form.submit class: "btn btn--primary" %>
  </div>
<% end %>

dropzone.css

@import url("https://esm.sh/[email protected]/dist/dropzone.css");

.dropzone {
  border-radius: var(--rounded-xl);
  border: 2px dashed var(--color-border);
  padding: var(--size-2);

  .dz-preview.dz-image-preview {
    background: transparent;
  }

  .dz-preview .dz-error-message {
    background: var(--color-negative);
    word-break: break-all;
  }

  .dz-preview .dz-error-message::after {
    border-bottom: 6px solid var(--color-negative);
  }

  .dz-preview:has(.dz-remove) .dz-error-message  {
    top: 148px;
  }
}

dropzone_controller.js

import { Controller } from "@hotwired/stimulus"
import { DirectUpload } from "https://esm.sh/@rails/[email protected]?standalone"
import Dropzone from "https://esm.sh/[email protected]?standalone"

export default class extends Controller {
  static values = {
    url: String,
    paramName: String,
    maxFiles: { type: Number, default: null },
    maxFilesize: { type: Number, default: 256 },
    acceptedFiles: { type: String, default: null },
    addRemoveLinks: { type: Boolean, default: true }
  }

  connect() {
    this.dropZone = this.#createDropZone()
    this.dropZone.enqueueFile = it => this.#upload(it)
  }

  disconnect() {
    this.dropZone.destroy()
  }

  #createDropZone() {
    return new Dropzone(this.element, {
      url: this.urlValue,
      paramName: this.paramNameValue,
      maxFiles: this.maxFilesValue,
      maxFilesize: this.maxFilesizeValue,
      acceptedFiles: this.acceptedFilesValue,
      addRemoveLinks: this.addRemoveLinksValue
    })
  }

  #upload(file) {
    new Uploader(file, this.dropZone).start()
  }
}

class Uploader {
  constructor(file, dropZone) {
    this.file = file; this.dropZone = dropZone;
  }

  start() {
    this.#createDirectUpload((error, blob) => {
      if (error) {
        this.#emitDropzoneError(error)
      } else {
        this.#createHiddenInput(blob.signed_id)
        this.#emitDropzoneSuccess()
      }
    })
  }

  directUploadWillStoreFileWithXHR(xhr) {
    this.file.xhr = xhr
    this.#bindProgress()
    this.#emitDropzoneProcessing()
  }

  #createDirectUpload(callback) {
    new DirectUpload(this.file, this.dropZone.options.url, this).create(callback)
  }

  #createHiddenInput(signedId) {
    this.hiddenInput = document.createElement("input")
    this.hiddenInput.type = "hidden"
    this.hiddenInput.name = this.dropZone.options.paramName
    this.hiddenInput.value = signedId
    this.file.previewElement.appendChild(this.hiddenInput)
  }

  #bindProgress() {
    this.file.xhr.upload.addEventListener("progress", it => this.#directUploadDidProgress(it))
  }

  #directUploadDidProgress(event) {
    this.dropZone._updateFilesUploadProgress([this.file], this.xhr, event)
  }

  #emitDropzoneProcessing() {
    this.file.status = Dropzone.PROCESSING
    this.dropZone.emit("processing", this.file)
  }

  #emitDropzoneSuccess() {
    this.file.status = Dropzone.SUCCESS
    this.dropZone.emit("success", this.file)
    this.dropZone.emit("complete", this.file)
  }

  #emitDropzoneError(error) {
    this.file.status = Dropzone.ERROR
    this.dropZone.emit("error", this.file, error)
    this.dropZone.emit("complete", this.file)
  }
}

Any ideas about progress for multiple files?

Rails' DirectUpload seems to be an extremely old and shity js-code, which does not even emit events (wtf).

@ktimothy

The example above actually implements progress. I am using it with multiple files and the progress events are working fine.

Is there a quick way to not have the controller overwrite the existing files? With my plain form files input I was doing something like this:

https://stackoverflow.com/questions/59803964/what-is-the-correct-way-to-update-images-with-has-many-attached-in-rails-6

        if params[:location][:files].present?
          params[:location][:files].each do |image|
            @location.files.attach(image)
          end
        end

This would just add new files to the existing ones which is what I am looking for. Now I could add another controller in this case as this page has just the files for the parent model and no other parent model attributes.

Side question in my code above I was going to add a turbo append to each attach and do a live update to the page showing the files added (setting auto-queue to true). Can you some how add this via drop zone?

@lohannon

Did you have to change anything in the view? I'm getting the same error even after making the changes you suggest.

@tfolk I also had to overwrite some method signatures to include the token and attachment name like this:

class DirectUploadController {
  constructor(source, file, token, attachmentName) {
    this.directUpload = createDirectUpload(file, source.url, token, attachmentName)
    this.source = source
    this.file = file
  }
  ...
  }

and

// Top level...
function createDirectUploadController(source, file, token, attachmentName) {
  return new DirectUploadController(source, file, token, attachmentName)
}

function createDirectUpload(file, url, token, attachmentName) {
  return new DirectUpload(file, url, token, attachmentName)
}

@lohannon I'll give it a try. Thanks.

Does anyone know what is the best way to display the files already uploaded in edit case? Thanks

This implementation does not actually work! Sure it works for the new action, but in the edit action, controller can not find form elements and a never ending rigmarole of JS and Stimulus... never ending! Does't work! We waste all this time implementing basics over and over, while in reality if you don't come from money and big teams, and you're working solo on a project, it means you will spill your guts working on the basics and working on the complex.